.\" FreeBSD version Copyright (c) 1996
.\"	Mike Pritchard <mpp@FreeBSD.org>.  All rights reserved.
.\"
.\" Adapted from share/man/man8/man8.hp300/crash.8
.\"
.\" Copyright (c) 1990, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.Dd July 25, 2025
.Dt CRASH 8
.Os
.Sh NAME
.Nm crash
.Nd FreeBSD system failures
.Sh DESCRIPTION
This section explains a bit about system crashes
and (very briefly) how to analyze crash dumps.
.Pp
When the system crashes voluntarily it prints a message of the form
.Bl -diag -offset indent
.It "panic: why i gave up the ghost"
.El
.Pp
on the console, and if dumps have been enabled (see
.Xr dumpon 8 ) ,
takes a dump on a mass storage peripheral,
and then invokes an automatic reboot procedure as
described in
.Xr reboot 8 .
Unless some unexpected inconsistency is encountered in the state
of the file systems due to hardware or software failure, the system
will then resume multi-user operations.
.Pp
The system has a large number of internal consistency checks; if one
of these fails, then it will panic with a very short message indicating
which one failed.
In many instances, this will be the name of the routine which detected
the error, or a two-word description of the inconsistency.
A full understanding of most panic messages requires perusal of the
source code for the system.
.Pp
The most common cause of system failures is hardware failure, which
can reflect itself in different ways.
Here are the messages which
are most likely, with some hints as to causes.
Left unstated in all cases is the possibility that hardware or software
error produced the message in some unexpected way.
.Pp
.Bl -diag -compact
.It Mounting from <device> failed with error <err>
The system was unable to mount the configured root filesystem.
Either the root filesystem has been corrupted,
or the system is attempting to use the wrong device as root filesystem.
.Pp
This is not a panic message; rather it is followed by an interactive
.Sy mountroot>
prompt where the operator can list detected devices and filesystems,
and select an alternative root filesystem to mount.
Alternatively, the system can be booted from recovery media to repair
the situation.
The system install media provides a live environment which is suitable
for this task.
.Pp
.It "init: not found"
This is not a panic message, as reboots are likely to be futile.
Late in the bootstrap procedure, the system was unable to locate
and execute the initialization process,
.Xr init 8 .
The root file system is incorrect or has been corrupted, or the mode
or type of
.Pa /sbin/init
forbids execution or is totally missing.
.Pp
.It "ffs_realloccg: bad optim"
.It "ffs_valloc: dup alloc"
.It "ffs_alloccgblk: cyl groups corrupted"
.It "ffs_alloccg: map corrupted"
.It "blkfree: freeing free block"
.It "blkfree: freeing free frag"
.It "ifree: freeing free inode"
These panic messages are among those that may be produced
when file system inconsistencies are detected.
The problem generally results from a failure to repair damaged file systems
after a crash, hardware failures, or other condition that should not
normally occur.
A file system check will normally correct the problem.
.Pp
.\" .It "trap type %d, code = %x, v = %x"
.\" An unexpected trap has occurred within the system; the trap types are:
.\" .Bl -column xxxx -offset indent
.\" 0	bus error
.\" 1	address error
.\" 2	illegal instruction
.\" 3	divide by zero
.\" .No 4\t Em chk No instruction
.\" .No 5\t Em trapv No instruction
.\" 6	privileged instruction
.\" 7	trace trap
.\" 8	MMU fault
.\" 9	simulated software interrupt
.\" 10	format error
.\" 11	FP coprocessor fault
.\" 12	coprocessor fault
.\" 13	simulated AST
.\" .El
.\" .Pp
.\" The favorite trap type in system crashes is trap type 8,
.\" indicating a wild reference.
.\" ``code'' (hex) is the concatenation of the
.\" MMU
.\" status register
.\" (see <hp300/cpu.h>)
.\" in the high 16 bits and the 68020 special status word
.\" (see the 68020 manual, page 6-17)
.\" in the low 16.
.\" ``v'' (hex) is the virtual address which caused the fault.
.\" Additionally, the kernel will dump about a screenful of semi-useful
.\" information.
.\" ``pid'' (decimal) is the process id of the process running at the
.\" time of the exception.
.\" Note that if we panic in an interrupt routine,
.\" this process may not be related to the panic.
.\" ``ps'' (hex) is the 68020 processor status register ``ps''.
.\" ``pc'' (hex) is the value of the program counter saved
.\" on the hardware exception frame.
.\" It may
.\" .Em not
.\" be the PC of the instruction causing the fault.
.\" ``sfc'' and ``dfc'' (hex) are the 68020 source/destination function codes.
.\" They should always be one.
.\" ``p0'' and ``p1'' are the
.\" VAX-like
.\" region registers.
.\" They are of the form:
.\" .Pp
.\" .Bd -ragged -offset indent
.\" <length> '@' <kernel VA>
.\" .Ed
.\" .Pp
.\" where both are in hex.
.\" Following these values are a dump of the processor registers (hex).
.\" Finally, is a dump of the stack (user/kernel) at the time of the offense.
.\" .Pp
.It "init died (signal #, exit #)"
The system initialization process has exited with the specified
signal number and exit code.
This is bad news, as no new users will then be able to log in.
Rebooting is the only fix, so the
system just does it right away.
.El
.Pp
That completes the list of panic types you are likely to see.
.Pp
If the system has been configured to take crash dumps (see
.Xr dumpon 8 ) ,
then when it crashes it will write (or at least attempt to write)
an image of memory into the back end of the dump device,
usually the same as the primary swap
area.
After the system is rebooted, the program
.Xr savecore 8
runs and preserves a copy of this core image and the current
system in a specified directory for later perusal.
See
.Xr savecore 8
for details.
.Pp
To analyze a dump you should begin by running
.Xr kgdb 1 Pq Pa ports/devel/gdb
on the system load image and core dump.
If the core image is the result of a panic,
the panic message is printed.
For more details consult the chapter on kernel debugging in
the
.%B "FreeBSD Developers' Handbook"
.Pq Pa https://www.freebsd.org/doc/en/books/developers-handbook/ .
.Sh SEE ALSO
.Xr kgdb 1 Pq Pa ports/devel/gdb ,
.Xr dumpon 8 ,
.Xr reboot 8 ,
.Xr savecore 8
.Sh HISTORY
The
.Nm
manual page first appeared in
.Fx 2.2 .
